1. Field of the Invention
This invention relates generally to multi-chip modules and, more specifically, to a LOC module having semiconductor dice attached to both sides of the module. A plurality of apertures formed in the module substrate allows passage of wire bonds from the active surface of the semiconductor dice attached to the bottom surface of the module through the substrate to connections on the top surface of the substrate. In addition, a plurality of chips is attached and electrically connected to the top surface of the substrate.
2. State of the Art
High performance, low cost, increased miniaturization of components, and greater packaging density of integrated circuits have long been the goals of the computer industry. Greater integrated circuit package density, for a given level of component and internal conductor density, is primarily limited by the space available for die mounting and packaging. For lead frame mounted dies, this limitation is, to a great extent, a result of conventional lead frame design.
A leads-over-chip (LOC) integrated circuit (IC) typically includes a semiconductor die (die) electrically attached to a LOC lead frame. In such an arrangement, the lead frame includes a plurality of lead fingers that extend over and are attached to the active surface of the die. The lead fingers are electrically connected to inputs and outputs (I/Os) or bond pads on the active surface and connect the die to external circuitry located on a substrate or other carrier. Moreover, the lead fingers actually provide physical support for the die. The lead frame and die are typically encapsulated within a plastic package, although ceramic and metal packages may also be used depending on the operating environment and the packaging requirements of the die.
With ever increasing demands for miniaturization and higher operating speeds, multi-chip module systems (MCMs) become increasingly attractive in a variety of applications. Generally, MCMs may be designed to include more than one type of die within a single package, or may include multiples of the same die, such as the single in-line memory module (SIMM) or dual in-line memory module (DIMM). MCMs which contain more than one die can help minimize operational speed restrictions imposed by long connection traces between cooperating components by combining, for example, the processor, memory, and associated logic into a single package on a single printed circuit board or other substrate or carrier. In addition, MCMs offer packaging efficiency.
MCMs typically comprise a planar printed circuit board (PCB) or other die carrier substrate to which a plurality of semiconductor dice are attached. Laminated substrates such as FR-4 boards are included in the term PCB as used herein, as are ceramic and silicon substrates, although the latter constructions are at this time less common as MCM carrier substrates. The semiconductor dice are typically wire bonded, TAB-connected or flip chip bonded (by an array of solder or other conductive bumps or conductive epoxies) to the PCB. An MCM configuration typically allows semiconductor dice to be bonded to one side only of the carrier substrate. Moreover, for semiconductor dice that are wire bonded to the PCB, the bond wires extend from the top surface of each die mounted on one side of the PCB by its back side to the plane of the PCB surface on that side, requiring longer wires to be used to connect the dice to the PCB traces than if the active surfaces of the dice were closer to the PCB surface. This often leads to undesirable parasitic electrical characteristics.
Therefore, a need exists for an MCM that provides for increased densification by bonding chips to both sides of the PCB, while providing for shorter wire bonds between wire bonded dice and the MCM PCB.